1. Field of the Invention
The present invention pertains to nuts, and more particularly, it pertains to a wing nut for fastening a vehicle wheel to the rotatable shaft of a wheel balancer or other wheel rotating apparatus.
2. Description of the Prior Art
Whell balancing machines having a horzontally projecting rotatable spindle have been used in the automotive servicing industry for a number of years. It is desirable on such machines to be able to mount the wheel directly on the horizontal spindle in a manner such that the spindle projects through the center hole of the wheel with the wheel being positioned against an abutting surface that is rotatable with the spindle. The wheel can then be secured by means of a single nut threaded directly onto the spindle rather than by securing numerous individual lug nuts. Such a wheel mounting apparatus is disclosed in U.S. Pat. No. 3,889,542 to Carrigan issued June 17, 1975.
The above-mentioned prior art displays two objectionable features. First, when securing the wing nut in order to firmly position the wheel on the spindle, the friction between the nut and the wheel makes it difficult to adequately tighten the nut. Failure to adequately tighten the nut often brings about a second problem during operation of the balancer. Normally, rotational force is transmitted to the wheel through a backing plate and a retainer cup which hold the opposite faces of the wheel (see FIG. 1 of the drawings herein, items 27 and 24 respectively). If, however, the nut has not been adequately tightened, the friction between said holding members and the wheel may be insufficient and the wheel may slip relative to the rotary motion of the spindle. When this occurs, the inertia of the wheel is transmitted to the nut through the retainer cup and the nut is prevented from rotating at the same angular velocity as the spindle. In this manner, the nut will unthread and may disengage from the spindle.